A photographic element in general comprises a support made of, for example, cellulose triacetate, or polyethylene terephthalate, or polyethylene naphthalate, or paper. Except X-ray films that have photographic emulsion layers on both sides of the support, most photographic elements have the light sensitive emulsion layers only on one side of the support through the use of adhesion promotion subbing layers or antihalation subbing layers. The side contaning light sensitive emulsion layers (emulsion side) may also optionally contain various other layers such as interlayers, filter layers, and surface protective layers. The side without light sensitive emulsion layers is in general called the backside. The backside is normally provided with an auxiliary layer such as an antihalation layer, or an antistatic layer or an anti-curling layer, or a surface protective overcoat layer.
The surface protective layer on the emulsion side often comprises hydrophilic binders such as gelatin, for example. During the handling of photographic elements, such as coating, drying, finishing, winding, rewinding, printing, and so on, the material surfaces are often harmed by contact friction with apparatus parts and between the front and back surfaces of the element. For example, scratches or abrasion marks can be brought about on the emulsion and backsides of a photographic material. These scratches and abrasion marks can deface the image during printing and projecting processes. On irreplaceable negatives, the physical scratches or surface damages require very expensive retouching.
There have been various proposals to obtain a physically improved photographic material by increasing the abrasion and scratch resistance of the overcoat layer, or by reducing the contact friction of the photographic material to other surfaces so that it will not be damaged during the manufacturing, exposure, developing, and printing or projecting processes. For example, methods for reducing the contact friction include incorporating both a silicone fluid and a surface active agent into the protective overcoat; using a mixture of dimethyl silicone and diphenyl silicone on the backside of the support; incorporating a triphenyl terminated methyl phenyl silicone into the emulsion protective overcoat; using a combination of dimethyl silicone and beta-alanine derived surfactants; using modified sperm oils in the protective overcoat; or using liquid organopolysiloxane with methyl and alkyl or aryl, or aralkyl side groups in the protective overcoat.
A more serious problem is the formation of the so-called static marks, caused by the accumulation of electrostatic charges that are discharged before processing the photographic element. The light-sensitive emulsion layers are then exposed to light generated by the discharge. Furthermore, the attainment of dust or dirt on the surface of a photographic element can also cause serious problems after development. For example, when the images from a negative film are printed on a positive film or a photographic paper, the existence of dust or dirt on the surface of the negative film will affect the formation of the print images.
Undesirable static discharges during manufacture, exposure, and processing of a photographic element can be controlled by modification of the surface charging characteristics. Matting agents can reduce the electrostatic charging by reducing the effective area of surface making contact. Surfactants or polymers of various kinds and combinations are employed very often to balance or reduce the surface contact charge as has been disclosed, for example, in U.S. Pat. Nos. 3,589,906, 3,666,478, 3,884,609, 3,888,678, 4,330,618, and others. Commonly used surfactants or polymers for static charge control include, for example, cationic and anionic fluorinated surfactants, polymeric quaternary ammonium salts, and the like.
Finely divided powdered grains or matting agents (beads larger than 500 nm) are often incorporated into the surface protective layer to increase the surface roughness and prevent contact and subsequent sticking. It is desirable that these matte beads are non-hydrophilic and consequently they are composed of materials different from the hydrophilic binders. Because of the different composition, these matte beads may have different refractive index. When light is passed through the photographic element, such as in photographic printing or projection, both the increased surface roughness and difference in refractive index can cause a non-uniform light path and result in graininess in photographic prints or mottle in projected images. For this reason, manufacturers have been using a large amount of non-process surviving (soluble) mattes, designed to solublize in high pH solutions, in combination with a small amount of process surviving (permanent) matte. High concentrations of processing removable matte are used especially when the unprocessed photographic elements are used or stored at high relative humidity and at elevated temperatures of from 30.degree. to 40.degree. C. High concentrations of soluble matte are also used to prevent contact specks that cause adverse sensitometric defects when the materials are rolled up.
The use of a high level of processing removable matte provides a satisfactory solution to conventional films for amateur use, for which the processed, or developed, film strips are returned to the consumer in synthetic resin pouches, or sleeves, where the frontside and backside of the film do not come in contact with each other.
Recent patents have disclosed photographic systems where the processed element may be re-introduced into the cassette. This system allows for compact and clean storage of the processed element until such time when it may be removed for additional prints or to interface with display equipment. Storage in the roll is preferred to facilitate location of the desired exposed frame and to minimize contact with the negative. U.S. Pat. No. 5,173,739 discloses a cassette designed to thrust the photographic element from the cassette, eliminating the need to contact the film with mechanical or manual means. Published European Patent Application 0 476 535 A1 describes how the developed film may be stored in such a cassette. The dimensions of such a so-called thrust cassette require that the processed photographic element is wound tightly and under pressure, causing direct close contact between the front and back sides which results in ferrotyping, especially at high temperature and high relative humidity. Processing removable matte does not prevent this problem.
In recent years, rapid processing and high temperature drying after processing have become common practice for photographic materials. The high temperature dried films, for example 60.degree. C. (harsh drying), tend to aggravate the ferrotyping which results from close contact, especially under elevated humidity and temperature. When ferrotyping is sufficiently severe, the resulting prints are unacceptable. Films dried at lower temperatures, for example 40.degree. C. (mild drying), tend to show much less ferrotyping. The reason for this difference is not understood.
It is known to use synthetic polymer particles in a silver halide photographic element to improve physical characteristics. In particularly, water dispersible polymer particles obtained by emulsion polymerization technique (polymer latex particles) have found wide use as partial replacement for gelatin. Many latex polymers, however, are incompatible or unstable for effective coating in protective layers coated from hydrophilic colloid solutions such as gelatin solutions which include various addenda as described above. These addenda, especially coating surfactants and antistatic control surfactants or polymers, can significantly reduce the stability of polymer latex particles, for example, by reducing the electrostatic repulsion force from the interaction between electrical double layers, or surface charges on the particles. Surfactants or charge control polymers can carry opposite charges to those on the polymer latex particle surface leading to latex particle flocculation through charge neutralization.
It has been heretofore known to employ latex polymer particles in photographic elements that are compatible with gelatin. However, they have been found to frequently provide unacceptable post-process ferrotyping protection, especially for elements having magnetic recording layers which are reintroduced into a cassette after processing.